This invention relates to electronic computer systems and techniques, and more particularly relates to improved methods and apparatus for clearing the memory section of a video-type computer and the like.
It is well known that a computer system conventionally employs a CRT section and the like to exhibit output data, and that such a system conventionally includes a storage circuit of suitable design for receiving and holding data signals prior to transfer to the video section. It is further conventional to employ a bit-mapped memory unit or chip for this purpose, in order that the memory cells in the chip will each correspond to one of the pixels on the CRT screen.
It will readily be apparent that, in such a system, the memory section must first be cleared of all residual or "old" data, i.e. initialized, before "new" data may be fed into the system. Since each cell in the memory is a separate storage unit, this means that all 65,536 cells in a so-called "64K memory" chip must be cleared by the insertion of a preselected data signal (usually a zero).
Clearing such a memory section is a time-consuming task, at least by computer standards, since each cell must be separately and sequentially addressed, and new "clearing data" written in, on a cell-by-cell basis until the entire operation has been completed. Unless this is done, the image which is projected onto the CRT screen will not only be composed of valid data signals but will also include other spurious unwanted data signals.
As explained in a co-pending U.S. patent application Ser. No. 427,236 filed Sept. 29, 1982 by McDonough, Laffite and Hughes, now U.S. Pat. No. 4,562,435, there has been an on-going market demand for video-type computers which present images of greater resolution. This can only be achieved, of course, by employing CRT screens having an increased number of pixels, and this, in turn, has required the use of storage sections having a correspondingly increased number of separate memory cells. As a consequence, it has increased the length of time required to clear the memory in the computer.
These disadvantages of the prior art are now minimized or overcome by the present invention, and novel methods and apparatus are provided for effectively clearing the memory of a computer system in a fraction of the time previously required.